Combined illuminating and germicidal lamp and method of making the same



944. J. L. LIBBY 2,362,384 COMBINED ILLUMINATING AND GERMICIDAL LAMP AND METHOD OF MAKING THE SAME Filed March 30, 1942 QzMMQ/Z Ju/Fs L. Lzbby Patented Nov. 7, 1944 COMBINED ILLUMINATING AND GERMI- CIDAL LAMP AND METHOD OF MAKING THE SAME Jules 1. Libby, Elgin, 111. Application March 30, 1942, Serial No. 436,752

1 Claim.

vgether with a small quantity of mercury; and

electrodes at opposite ends of the envelope connectible with a source of energizing current for ionizin the gaseous contents of the lamp and producing a discharge within the tube between its electrodes.

Ordinary illuminating lamps or tubes of this. nature have a coating of a fluorescent phosphor on the entire inside surface of the glass envelope which compound is excited by the ultra-violet light typical of the mercury spectrum created upon discharge of the tube and caused to fluoresce thereby to provide a source of light for illuminating purposes.

It is common knowledge to those skilled in the art that such gas discharge illuminating lamps are superior to the incandescent filament lamp most commonly used at the present time. The quality of the light produced by gas discharge lamps and their economy of operation makes them ideally suited for use in industry.

Wherever food products are handled, processed or packaged, however, it is important to render the food products as sterile as possible. To this end germicidal lamps have come into widespread use in the food industry; Germicidal lamps are similar to the ordinary gas discharge illuminatin lamp and are used in con- Junction with the illuminating lamps in the manufacture of many food products.

Germicidal'lamps are also particularly useful in public places, ofilces, factories, and the like, where they act to destroy air-borne bacteria and thus remove a common cause of infection.

The tube of a, germicidal lamp fixture, like that of the gas discharge illuminating lamp fixture, essentially consists of a glass envelope having sealed therein under low pressure an inert gas and a quantity of mercury, and employs electrodes at the ends of the envelope to effect ionization of the gas contents of the lamp to produce radiant energy in the form of ultraviolet light for sterilization of the food products or for disinfecting purposes. However, the glass envelopes of such germicidal lamps are of special glass capable of enabling ultra-violet light waves to pass therethrough and impinge the food products subjected to the lamps.

Thus while ultra-violet light waves are created by the discharge in both types of tubes, the nature of the glass envelope and the fluorescent phosphor compound thereon in the illuminating tube precludes the passage of ultra-violet light therethrough.

Because of this fact, present equipment in the food industry consists in conventional fluorescent, lighting fixtures and separate ultra-violet light; fixtures, the first designed to provide a source of illumination and the latter providing a source of ultra-violet light capable of killing bacteria, germs and the like.

The resulting duplication of lighting fixtures is obviously objectionable.

The present invention has as its main object to eliminate the necessity for duplication of light fixtures in the food industry through the provision of a single gas discharge lamp capable of emanating both luminous energy for illuminatwing purposes and radiant energy in the form of ultra-violet light for sterilizing purposes.

More specifically, this invention has as its object the provision of a gas discharge lamp or tube, the envelope of which is formed of special glass to enable ultra-violet light waves to pass therethrough and which has predetermined portions thereof coated with a fluorescent phosphor compound to provide a source of illumination in addition to a source of ultra-violet light for sterilizing and disinfecting purposes.

Another object of this invention resides in the provision of a simple method for making a combined illuminating and germicidal gas discharge lamp of the character described.

With the above and other objects in view, which will appear as the description proceeds,

this invention resides in the novel method and in the novel combination and arrangement of mechanical expedients for carrying the same into eiTect, substantially as hereinafter described, and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claim. v

The accompanying drawing illustrates two complete examples of the physical embodiment of the invention constructed according to the best modes so far devised for the practical application of the principles thereof, and inwhich:

Figure 1 is a side elevational view of the complete gas discharge lampembodying theprinciples of this invention;

Figures 2, 3 and 4 are perspective views of the special glass envelop illustrating the first two steps in the method of making the same:

Figure 5 is a diagrammatic view illustrating the final step in the method of making the envelop of the tube; and

Figure 6 is a view similar to Figurel illustrating a modified form of lamp.

Referring now particularly to Figure 1 o! the accompanying drawing, the numeral l0 designates generally a gas discharge lamp or tube the envelope ll of which is constructed in accordance with the principles of this invention. The envelope I l is made from a piece of glass tubing of substantial length as compared to the diameter of the tube.

Plugs I 2 cover the seals at the opposite ends of the envelop which confine therein under low pressure a quantity of inert gas of the type used in gas dischargetubes for illuminating purposes and a small amount of mercury.

The plugs I! carry prongs IS on their exteriors adapted to be received in suitable sockets (not shown) and electrodes ll interiorly of the envelope. As is customary, the impression of a suitable high voltage current across the electrodes ll of the tube produces a discharge within the envelope to create amercury spectrum which provides a source of radiant energy in the form of ultra-violet light.

s Inasmuch as the gas discharge tube of this invention is designed to provide a source of both luminous energy for illuminating purposes and radiant energy in the form of ultra-violet light aacasu fluorescent phosphor band any desired area of the tube may be coated merely by variation in the pitch of the spiral.

Consequently. any selected quantity of ultraviolet light may be obtained by regulation of the area of clear window space on the envelope, and

'such quantities of ultra-violet light which are detrimental to the human body or to certain proc- -eases may be readily avoided.

One method of making the envelope for the combined illuminating and germicidal lamp is as as shown in Figure 3. Any suitable manner of introducing the powder into the envelope may be employed. The envelope having its interior surfaces thus coated with fluorescent phosphor material is heat treated to effect a degree of bonding of the phosphor material to the glass wall of 'v the tube, which 'heat treating step may if desired be carried out in an oven l8, such as shown in Figure 4.

After the fluorescent phosphor compound has i been baked onto the inner wall of the tube in this manner, portions of the coating are removed to form the clear window portions IS on the tube for sterilizing and disinfecting purposes, it is essential that the glass envelope be formed of a special glass capable of passing ultra-violet light waves therethrough. These ultra-violet light rays are produced in all gas discharge lamps used for illuminating purposes which employ mercury vapor, but the major portion of the waves are prevented from passage through the walls of the glass envelope due to the customary coatings of fluorescent phosphor on the interior surfaces Of the envelope and due to the nature Of the glass itself.

In illuminating tubes, the entire interior of the envelope l l is coated with a fluorescent phosphor material which is excited by the ultra-violet light waves created upon energization and discharge of the tube and caused to fluoresce, which fluorescence is utilized for illumination.

coated with a fluorescent phosphor material so through which the ultra-violet light created by the discharge of the tube passes.

Although any suitable manner maybe employed for removing portions of the phosphor coating it has been found desirable from the standpoint of controlling the proportions of coated and uncoated portions on the envelope to rotate the envelope at a uniform rate while a scrap. ing tool or wheel i9 is passed longitudinally through the tube from one end to the other in contact with the inner wall of the tube as shown at 20 in Figure 5.

r the tube, which of course, is desirable as an excessive quantity is injurious to humans and as indicated in Figure 5 the clear area should not ex. ceed substantially one-half of the total area.

As will be apparent, longitudinal motion of the tool l9 through the tube in contact with the inner wall thereof results in the formation of adjacent spirals of coated and uncoated portions of the envelope along its entire length. 1

After the tube has been treated for the removal of portions of the phosphor compound, it may be completed in a manner well known to the art and which includes sealing a quantity of an inert gas and mercury inside the envelope under low presthat relatively large coated portions l5 and un- 3 coated portions I 5 occur throughout the length of the tube.

The uncoated portions i6 act as windows through which the ultra-violet light rays created upon energization of the lamp pass to impinge and sterilize any food products subjected to the rays of the lamp.

As will be apparent, any desired proportions besure and applying the plugs H to the ends of the tube.

While a hot cathode type of gas discharge tube has been illustrated in Figure l of the drawing, it will be readily apparent that this invention is also adaptable to gas discharge tubes of the cold cathodetype.

For small-wattage consumption, the lamp construction illustrated in Figure 6 has been found desirable. In this embodiment of the invention an .outer envelope H which may have a shape similar to conventional incandescent bulbs of lamps encloses a small gas discharge tube II. The tube H is bent to approximately U-shape and has its ends provided with electrodes 14' electrically connected to a screw plug 22 at the sealed end of the outer bulbous enclosure. Both the tube II' and the enclosure 2| are of special glass through which ultra-violet light may pass.

In this instance, however, interior portions of the outer bulbous enclosure are coated with the fluorescent phosphor compound as at IS, with only the lower half of the bulb 2| coated so that ultra-violet light created by the discharge tube H passes through the upper half of the bulb adjacent to its sealed end.

From the foregoing description taken in connection with the accompanying drawing, it will be readily apparent that this invention provides a combined illuminating and germicidal tube or lamp for gas discharge lamp fixtures whereby single fixtures employing one or more such tubes are capable of supplanting the dual lighting fixtures in use at the present time; and that the method for making the lamp 01' this invention is extremely desirable due to its simplicity.

What I claim as my invention is:

In a combined germicidal and illuminating lamp: a single glass envelope constituting the sole enclosure of the lamp and through which ultraviolet radiations in the bactericidal band of the ultraviolet portion of the spectrum may pass; means at low pressure within the envelope for producing ultraviolet bactericidal radiations; and a sprial band of fluorescent material on the interior surface of the glass envelope covering an area less than the total area of the envelope and extending substantially from one end of the envelope to the other, the pitch and width of the spiral band being such as to leave a spiral band of clear glass substantially no greater in area than half the total area of the envelope, whereby the lamp radiates luminous and bactericidal energy through said single envelope.

JULES L. LIBBY. 

